Past Papers 2012&2013 Flashcards
Is kWh/yr is a unit of energy?
False
The fundamental units of energy are kg/ms2
False, should be kgm^2/s^2
Individuals hold different viewpoints on the purpose and challenge of creating a sustainable energy supply system. Identify 3 such viewpoints
Viewpoints:
● Human well-being(moral obligation)
● Climate change limitation(save the planet)
● Environment Protection(biodiversity)
● Fossil Fuel Prolongation(sustain economic growth)
● Fossil Fuel Replacement(pollution reduction)
● Security of Supply(political autonomy)
Individuals hold different viewpoints on the purpose and challenge of creating a sustainable energy supply system. Identify how they might be in conflict.
Conflicts
● Energy efficiency measures may worsen indoor air quality
● Decentralised power production reduces global emissions but moves them to
breathing zones
● Increased system complexity -> increased capital/operating/maintenance costs
Elaborate 2 approaches to demand reduction
be employed to create a sustainable energy system in the UK. In each case identify a principal
barrier.
- Use of district heating.
Barrier: Significant capital and continued investment, due to maintenance, required to ensure system robustness
- Unanimous use of biodiesel public transport.
Barrier: Although public transport would put
significantly less strain on the biofuel demand, changing human demands (personal transport) is
a challenge too great.
- Smart grids
Barrier: Requires high levels of communication between lowest levels of demand and higher levels of production, meaning likely high maintenance and general running
costs
- Microgeneration (all forms of microgeneration reduce demand) - CHP.
Barrier: To be considered as sustainable, the input fuel requires to come from a renewable source, such as
biofuels.
Elaborate 2 approaches to energy supply that may
be employed to create a sustainable energy system in the UK. In each case identify a principal
barrier.
- Combined renewable/storage solution. Barrier: Requires a significant investment to achieve the required infrastructure to balance supply, demand, storage and its associated losses, likely at the expense of the user.
- Coal replaced by biofuels. Barrier: Biofuel is not capable of outputting the same amount of power as coal, in MW/Kg, and regrowth has not yet been proven to be sufficient enough to consider biofuel as sustainable.
Give 3 substantial reasons why the renewable energy resource in the UK is likely to be substantially less than the total energy consumption.
● Most renewable sources are intermittent in their performance and it’s very unlikely that their peak supply times will coincide with times of peak demand.
● Demand in the UK is constantly changing, the electricity supply must be able to react immediately to changes in demand- not possible with a renewable supply.
● There are currently no storage capacity in the electricity network- storage would greatly increase the effectiveness of renewable supply.
What impact does climate change have on energy systems and what impact do energy
systems have on climate change?
(The persons answer)
●Climate change will tend to reduce the demand for heating energy while increasing the demand for cooling energy. The overall effect is predicted to be an increase in energy demand.
● The increased consumption of energy is raising temperatures in urban areas – the so-called heat island effect. Systems utilising fossil fuels produce emissions that contribute to (localised) ‘global warming’ and air pollution.
Identify 3 technological challenges facing the continued use of fossil fuels at present rates and give your view on likely effectiveness
1) refine exploration techniques;
2) make less ‘polluting’ (e.g. decarbonise);
3) enhanced extraction (e.g. sequestrate C);
4) new resources (e.g. coal bed methane, oil shale, tar sand);
5) new uses (e.g. methanol production).
Identify the principal emissions from fossil fuel combustion and state how the impact might
be mitigated.
Carbon Dioxide (CO2)
Environmental Problems:
Increasing global surface temperatures
Mitigate Impact: Carbon Capture and storage
Sulphur Dioxide (SO2)
Environmental Problems:
Concentration influences habitat stability for plant and animal communities. Causes acid rain
Mitigate Impact: I think this is the same as the Nitrous Oxides
Nitrous Oxides (NOx)
Environmental Problems:
Respiratory Problems
Mitigate Impact: Careful control of combustion process and treatment of exhaust gases using chemical action or filtration.
Soot - Causes haze
Mitigate Impact: DUNNO
With the aid of a diagram, explain the operation of a combined cycle gas turbine power plant, commenting on its thermal efficiency and how this might be improved.
● CCGT power stations have a secondary steam raising circuit using the heat from
the gas turbine exhaust.
● Conventional gas turbine systems (25-30% efficiency) with massive heat rejection
from exhaust
● CCGT systems (55-60% efficiency)
● Nat Gas used to fuel gas turbine - turbine exhaust temperature is high and
contains a great deal of energy; gases pass through heat exchanger to boil water
and produce steam, which then passes through the turbine that drives a second
generator.
Define Solar Declination
The angle between the equator and a line drawn from the centre of the earth to the centre
of the sun.
Define Solar Azimuth
The azimuth angle is the compass direction from which the sunlight is coming.
Define Solar Altitude
The angular height of the sun in the sky measured from the horizontal.
Define Solar Time
Reckoning of the passage of time based on the sun’s position in the sky. Units - Day
Ts – Tm = ± Ldiff/15 + (Et
/60) + ds
where, Ts = solar time Tm = local time Ldiff = longitude difference Et = equation of time ds = daylight saving time
(The second letter in each term is subscript)
Differentiate between isotropic and anisotropic sky conditions in the context of inclined surface solar irradiance prediction and state why the latter case gives rise to modelling
complexity.
Isotropic: Uniform brightness
Anistropic: Non-uniform brightness
Difficulty in calculating the diffuse component of solar heat gains
